Light alloy piston for rotary engines

ABSTRACT

A light alloy piston especially suited for rotary engines is provided with a ferrous ring gear and the hub portion of the piston is provided with equally spaced axially extending bores equal to the number of corners of the piston. Pins are secured in the bores and the end portions thereof extend beyond the face of the hub portion and form a close sliding fit with mating apertures or annular grooves in the ring gear. The ring gear is secured to the piston itself by screws.

United States Patent [191 Reitz et al. Apr. 9, 1974 LIGHT ALLOY PISTON FOR ROTARY 3,333,763 8/1967 .lungbluth et a1, 418/61 ENGINES 3,489,125 1/1970 Fend 418/61 3,655,302 4/1972 Hermes et a1 418/61 [75] Inventors: Johannes Reitz, Kirchhausen; Hans Jurgen Frese, Bad Friedrichshall, both of Germany [73] Assignee: Karl Schmidt Gmbl'l, Neckarsulm,

Germany 221 Filed: 1011.19.1972

21 App1.No.: 219,045

[30] Foreign Application Priority Data Feb. 10, 1971 Germany 2106280 52 us. c1. 418/61 A, 74/804 511 1111. c1. F01c 1/02, F04c 17/02, F16h 1/28 581- Field of Search 418/61; 123/8.01; 285/187;

[56] References Cited UNITED STATES PATENTS 3,400,604 9/1968 Jones 418/61 Primary Examiner-Carlton R. Croyle Assistant Examiner-John J. Vrablik Attorney, Agent, or lf rm -fiurgess, Dinltlage &

Sprung 57] ABSTRACT 2 Claims, 4 Drawing Figures ATENTEU APR 9 I974 SHEET 1 0F 2 1 LIGHT ALLOY PISTON FOR ROTARY ENGINES BACKGROUND This invention relates to a light alloy piston, preferably of an aluminum alloy for use in rotary piston internal-combustion engines, particularly the trochoid type. The piston is provided with a ring gear fixed on one side which consists of a ferrous material, preferably steel, and has internal teeth to control the rotation of the piston.

The ring gear of a rotary piston is usually a member which is made separately from the piston from ferrous material, preferably steel, and is positively joined to the piston by screws or pins or by welding. With such a joint, the different coefficients of thermal expansion between the piston and ring gear result in a more or less pronounced deformation of the ring gear. Because the conditions of interengagement between the ring gear and eccentric shaft vary continually in operation, the internal teeth of the ring gear are subjected to altemating stresses, which in areas of excessive stress concentrations may result in a fracture of the ring gear.

To eliminate these disadvantages, it is known from the published German Application No. l,8l7,l68 to reduce the heat transfer between pistons for rotary piston internal-combustion engines and ring gears by securing the ring gear to the piston with a heat-lagging insulating disc in between or providing it with a heatlagging covering or making it from ceramics, sintered material or plastics material.

Because it has been found that these drawbacks cannot be entirely eliminated by these measures, it is an object of this invention so to design the joint between the ring gear and the piston that a deformation or fracture of the ring gear caused by excessive stress concen-,

trations due to the different coefficients of heat expansion between the piston and .ring gear materials, is avoided.

SUMMARY This object is accomplished according to the invention by providing the hub portion of the rotary piston with a circular series of regularly angularly spaced, axially extending bores in a number which corresponds to the number of comers of the piston. Pins are secured in the bores and their end portions adjacent to the ring gear protrude from the end face of the hub portion and extend in a very close sliding fit into mating apertures of the ring gear which is secured to the piston by screws, preferably necked-down screws. The screws are provided in the same number as the pins'and are regularly angularly spaced in the hub portion of the piston.

DESCRIPTION OF THE DRAWINGS The accompanying drawings illustrate two embodiments of the invention wherein:

FIG. 1 is a side elevational view showing a trochoidtype light alloy rotary piston;

FIG. 2 is a sectional view taken along line II-II of FIG. 1;

FIG. 3 is a side elevational view similar to FIG. 1 illustrating further embodiments of the invention; and

FIG. 4 is a cross-sectional view taken along line IV-IV of FIG. 3.

DESCRIPTION In a development of the invention, the screws extend through the sleevelike pins and each of those end portions of the pins which protrude from the end face of the hub portion of the rotary piston toward the'rihg gear is provided with a collar, which serves as a slide block.

In a special feature of the invention, the pins are arranged in the relatively coldest regions of the hub portion of the rotary piston.

According to another feature of the invention, the hub portion of the rotary piston is provided on that end face which faces away from the ring gear with a plate, which consists preferably of steel and engages the ends of the pins and is provided with bores for the screws which serve to secure the ring gear. The heads of the screws are tightened against the plate to limit the axial movement of the sleevelike pins.

The ring gear and the plate are suitably spaced from the respective adjacent end face of the hub-portion by a distance which is at least equal to the axial thermal expansion of the hub portion so that there is a sufficiently large clearance in any operating condition. For

" directions during operation. This expansion will not change the common axis of the two members and will not result in undesired high stress concentrations in the ring gear. The pins which are secured in the hub portion of the rotary piston and which protrude from the end face of the piston facing the ring gear take up the axial forces which are exerted on the system owing to a non-uniform distribution of pressure on the piston faces and the external acceleration. As a result, a satisfactory joint between the piston and ring gear is ensured in operation. Besides, the pins compensate for the thermal expansion of the piston and ring gear in an axial direction. The fixation of the ring gear to the piston by means of necked-down screws has the advantage that the thermal expansion of the piston in an axial direction is taken up by the necked-downscrews. The

necked-down screws are self-locking and firmly connect the piston and ring gear even when they have been tightened only with a small torque but they do not hin- I I der the thermal expansion of the piston and ring gear independently of each other because the tightening torque can be selected so that the two components can slide independently of each other at their contacting surfaces. Force is transmitted from the piston to the ring gear by the pins and the radially extending sides of the apertures in the ring gear.

Referring now to FIGS. 1 and 2 of the drawing, three, regularly angularly spaced, axially extending bores 3 are formed in the hub portion 2 of the-piston and disposed on a circle. Pins 4 are secured in said bores and have end portions which protrude from the end face of the hub portion 2 toward the ring gear 6 having internal teeth and extend as a very close sliding fit in mating apertures 5 in said ring gear. The ring gear 6 is faced against the end face of the hub portion 2 of the piston I by three necked-down screws 7, which are disposed on the same circle as the pins 4 and closely adjacent thereto.

FIGS. 3 and 4 show a preferred design of the trochoid-type rotary piston 8 according to the invention. Three regularly angularly spaced, axial bores are disposed in the coldest regions of the hub portion 9 and sleevelike pins 1 l are secured in bores 10 and have end portions which face the ring gear 12 having internal teeth and which protrude from the end face of the hub portion 9 and are provided each with a collar 13, which slides as a very close fit in a mating aperture 16 of the ring gear 12. By means of three necked-down screws 14 extending in the sleevelike pins 11, the ring gear 12 is forced against the end face of the collars 13 of the pins 11. A steel plate 15 is secured to that end face of the hub portion-9 which is remote from the ring gear 12 and extends under the heads of the necked-down screws 14 and engages each of the sleevelike pins 11 at its end face which is remote from the collar.

What is claimed is:

1. Light alloy piston having a number of corners comprising ferrous ring gear means fixed on one side and having internal teeth to control the rotation of the piston, hub means having a circular series of regularly angularly spaced, axially extending bores in a number which corresponds to the number of corners of the piston, sleeve-like pin means secured in said bores and, at the ends adjacent to the ring gear, protruding from the end face of the hub means of the piston and extending in close sliding fit into mating apertures of the ring gear means, each end of said pin means protruding from the end face of the hub means toward the ring gear means being provided with integral collar means which serves as a slide block, said ring gear means being secured to the piston by screw means extending through said sleevelike pin provided in the same number as the pin means said hub means being provided on the end face remote from the ring gear means with plate means having bores for the screw means which secures the ring gear means and extends under the heads of said screw means and engages the ends of the pin means. 7

2. Light alloy piston of claim 1 wherein the ring gear means and the plate means are axially spaced from the adjacent end face of the hub-means by a distance which is at least equal to the axial thermal expansion of the hub means. 

1. Light alloy piston having a number of corners comprising ferrous ring gear means fixed on one side and having internal teeth to control the rotation of the piston, hub means having a circular series of regularly angularly spaced, axially extending bores in a number which corresponds to the number of corners of the piston, sleeve-like pin means secured in said bores and, at the ends adjacent to the ring gear, protruding from the end face of the hub means of the piston and extending in close sliding fit into mating apertures of the ring gear means, each end of said pin means protruding from the end face of the hub means toward the ring gear means being provided with integral collar means which serves as a slide block, said ring gear means being secured to the piston by screw means extending through said sleevelike pin provided in the same number as the pin means said hub means being provided on the end face remote from the ring gear means with plate means having bores for the screw means which secures the ring gear means and extends under the heads of said screw means and engages the ends of the pin means.
 2. Light alloy piston of claim 1 wherein the ring gear means and the plate means are axially spaced from the adjacent end face of the hub means by a distance which is at least equal to the axial thermal expansion of the hub means. 